Immunisation of mice with fractions derived from the intestines of Dirofilaria immitis

Antigens that are not normally seen by the host but that are nevertheless, accessible to host immune effector molecules and cells such as the native e ndoantigens associated with the intestinal epithelium of haematophagous tis sue-dwelling parasites, could be potentially useful vaccine antigens. In th is study, intestines were dissected from adult Dirofilaria immitis, homogen ised, and a 105000 x g pellet obtained and extracted with Triton X-100. The soluble 105000 x g supernatant from this extract induced partial protectio n (51%) against a challenge infection of third stage larvae (L3) implanted in micropore chambers. Sera from mice immunised with this soluble detergent extract reacted with proteins ranging in size from 38 to 130 kDa. Immunolo calisation studies indicated the mouse sera reacted primarily to the lumena l surface of the intestines of adult D. immitis, though reactivity to the l ateral nerve/epithelial chords, hypodermis and reproductive tracts was also noted, indicating the presence of shared antigens. Tissues of L3s were als o recognised by the immunised mouse sera. These mouse sera did not react to a dog blood fraction prepared identically to the D. immitis fraction. Only those sera from D. immitis-infected dogs with heavy or long-term infection s were reactive to a single 42 kDa protein. After 24 h incubation in fluore scein isothiocyanate-conjugated serum the intestinal tract of Onchocerca vo lvulus and D. immitis L3 and L4 fluoresced, indicating the serum had been i ngested. These data suggest that filarial gut-associated antigens (apart fr om the single 42 kDa antigen) are not seen by normally infected hosts, that they can be accessible to antibodies and that they can induce an immune re sponse which is partially protective. (C) 2001 Australian Society for Paras itology Inc. Published by Elsevier Science Ltd. All rights reserved.